The developmental neurobiological hypothesis which this proposal aims to test is whether the spinal cord growth and survival enhancement factor obtained from chick embryo muscle (3,4) can act as a cue to guide the direction of growth of chick embryo motor neurties. This factor has been shown to have stimulatory effects on spinal cord cell survival and neurite extension, but it is not known if this factor can influence the direction of motor neurite growth. In order to test the hypothesis of directed growth, dissociated cholinergic spinal cord neurones will be grown in vitro and the spinal cord factor obtained from chick myotubes will be applied to single axons or to the entire culture. Quantitative measurements of directionality of growth, neurite adherance and restricted or preferential areas of neurite growth will be made with the recently developed microperfusion and adherance measurement techniques. These techniques developed by myself and Dr. John Barrett (5,6) will allow quantitative measurements to be made which will determine if the spinal cord growth factor can, 1. guide motor neurite growth via a soluble gradient, substrate bound and/or adherance mechanisms, and 2. determine if different muscle sources of the factor affect separate populations of cholinergic spinal cord neurones. These experiments will serve as a basis for longer term objectives of continuing to study motor neurite growth in vitro and eventually applying the results of in vitro experiments to in vivo studies of motor axon guidance and axon-muscle specificity. The proposed studies are not immediately health related, but may indirectly serve as a basis of experimentation aimed at determining the mechanisms which result in incorrect motor axon guidance and axon-muscle specificity occurring after postnatal nerve damage.